The present invention relates to a method and apparatus for producing an uninterrupted flow of a uniformly subcooled liquid composed of a volatile fluid, for instance, a cryogenic liquid. More particularly the present invention relates to such a method and apparatus in which the saturated liquid is converted into a subcooled liquid by pressurization of the volatile fluid.
When a volatile fluid such as a cryogenic liquid is to be delivered from a storage tank or facility by piping, some distance from its origination, it is difficult to prevent the liquid from flashing and vaporizing due to pressure losses and/or heat leak in the piping. In order to prevent such flashing, it is known to lower the temperature of the liquid cryogen below the saturation temperature and to deliver the liquid cryogen in a subcooled state.
Prior art subcoolers, typically for liquid nitrogen, operate by delivering nitrogen as a saturated liquid or two-phase flow nitrogen to the subcooler at an operating pressure. A portion of the incoming flow is diverted and used to fill a reservoir that is maintained at or slightly above atmospheric pressure. The diverted flow is reduced in pressure through expansion to the saturation temperature of nitrogen at atmospheric pressure. The remainder of the nitrogen is routed through heat exchanger coils submerged in the reservoir, and, through heat exchange with the colder reservoir nitrogen, is reduced in temperature so that the nitrogen can be utilized as a subcooled liquid.
A major disadvantage of such a prior art subcooler is that the degree of subcooling achieved is variable depending upon process conditions. Additionally, a relatively large amount of the incoming nitrogen is vented to achieve the subcooling.
The present invention provides a subcooling method and apparatus by which a cryogen or any other volatile fluid can be subcooled in a controlled manner and with significantly reduced losses as compared with prior art subcooling techniques. Other advantages of the present invention will become apparent.